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XI. On the Purification ofJtapefeed Oil By C. Thenard*. 



1 O purify oil of rapefeed, mix ioo parts of the oil with 

 from I J- to is parts of iulphuric acid, and ftir the mixture. 

 The oil will immediately change its colour; it will become 

 turbid and afiume a blackifti-green tint, and at the end of 

 three quarters of an hour it will be full of flakes. You muft 

 then give over ftirring it, and add gradually double its weight 

 of water to remove the fulphuric acid, which, if allowed to 

 remain too long with the oil, would not fail to exercife too 

 ftrong an action on it, and to char it. The mixture muft 

 then be beat for at leaft half an hour, to bring the molecular 

 of the oil, the acid, and water, into contact with each other ; 

 after which it is to be left at reft. 



When it has retted about eight days, the oil will float on 

 the furface of the water, and the latter will itfelf float on a 

 black matter, precipitated from the oil by the fujphuric acid: 

 it is this matter which colours the oil, and prevents it from 

 burning with facility. Three very diftincl: ftrata, then, are 

 eftablifhed, as is here feen : the upper one is oil ; the feconcl 

 is aqueous, and contains a little fulphuric acid ; and the third 

 is carbonaceous. The oil which forms the upper ftratum, 

 after thefe eight days of reft, is far from being limpid : twenty 

 days, in my opinion, would be neceflary for it to purify itfelf 

 merely by repofe ; but by filtration it may be immediately 

 obtained perfectly clear and tranfparent. For this pur-x/e^ 

 pounded charcoal, and a piece of linen or cotton cloth, may 

 be employed : the two la it fubftances are preferable to any 

 other. The fame cloth will ierve feveral times, only it mutt 

 be carefully cleaned. 



By following this procefs with attention, you may obtain 

 oil which has much lefs colour, odour, and tafte, than that 

 commonly ufed ; which will burn with the greateft facility, 

 and without any refidu.um; and which is equal to the pureft 

 oil fold in the (hops, &:c. The lofs is very inconfiderable. 



If you are defirous of obtaining it ftill purer, it may be ex- 

 pofed again to the fame treatment; but, in that cafe, for ioo 

 parts of oil, one hundredth part of concentrated fulphuric acid 

 will be fufficient. The fulphuric acid will not form in oil 

 which has been once purified a blackifh precipitate; on the 

 contrary, it produces a very fcanty precipitate, of a grayifh- 

 white colour. This precipitate is more difficult to be feparat'e'd 

 than the former. 



' V,o:n JovrxiJ dt Vhyfique, Floreal, an. 9. 



When 



